The present invention relates to a counterbalance mechanism for a manipulator mechanism used with a laser knife device.
Most of the laser knives which have been developed are CO.sub.2 laser knives, that is, they operate with a CO.sub.2 light source. These CO.sub.2 laser knives are very similar to one another in their mechanical structure irrespective of their specific model or type. In these devices, a laser beam emitted by a CO.sub.2 laser source is transmitted through a light conducting mechanism having a flexible arm structure which has totally reflecting mirrors positioned in its articulation joints. The beam is focused to a small spot by a focusing lens provided at the end of the light conducting mechanism.
The construction of the conventional manipulator is generally as follows. The manipulator is provided with a long horizontal arm extending horizontally from a laser source and a long vertical arm extending downwardly from the end of the horizontal arm. At the juncture between the two arms, a flexible articulation such as described above is positioned. The end portion of the vertical arm is constructed of three flexible articulation each coupled to an arm. The last articulation coupled to the last arm in the sequence holds a focusing lens. The last arm corresponds to the handle of a knife and it is, in general, called "a handpiece". The operator holds and manupulates the handpiece to control the laser irradiation position. The long horizontal arm and the long vertical arm of the manipulator are used to move the end of the handpiece as desired there-dimensionally, up and down, right and left, and forward and backward. The three articulations at the end of the vertical arm are used to precisely and accurately control the position and direction of the irradiation point.
Examples of such a conventional manipulator are disclosed in the specifications of U.S. Pat. No. 3,913,582 and of Japanese Laid-Open Patent Application No. 94182/1974. The conventional manipulator has a flexible light conducting path with seven mirrors and eight arms one of which is a quite long horizontal arm. In order to maintain the horizontal arm horizontal, it is absolutely necessary to provide a counterbalance. Such a conventional manipulator will be described in detail below.
A first essential condition required for the manipulation is that its operation be smooth and light so that the operator can operate the handpiece smoothly and easily as if he was using an ordinary surgical knife. Any mechanism which fatigues the operator during a surgical operation which lasts for a long period of time is not acceptable. A second essential condition is that the manipulator be so designed that its arm is sufficently long to cover all the positions needed for different kinds of surgical operations.
An essential condition required for the counterbalance mechanism is that it be simple and have no protruding components. If the counterbalance mechanism does have such a protruding component, the operator or his helper may come into contact with it jarring the knife during an operation or the protruding component may strike an overhead operating lamp.
In order to meet the first condition required for the manipulator, it is necessary that, irrespective of the positions of the manipulator and handpiece, no reaction force due to the variations of their positions be applied to the operator's hand. In other words, it is necessary that, when the operator removes his hand from the manipulator which has been set in a desired position, the position of the manipulator thus set remain unchanged. Hereinafter, this will be referred to as "moment-free operation" when applicable. Especially, the horizontal arm of the manipulator, which moves both vertically and horizontally, needs a counterbalance mechanism which provides for moment-free operation of the manipulator.
In moving the vertical arm forwardly and backwardly, a second counterbalance mechanism is necessary for moment-free operation. However, the provision of the second counterbalance mechanism may be eliminated due to the following reasons. The rigidity of a part of the manipulator extending from the vertical arm may not be higher than that of the horizontal arm although the rigidity of the horizontal arm should of course be high enough to prevent bending of the horizontal arm under its own weight. Therefore, this part of the manipulator may be made light in weight. The stable, neutral position of this part will be in a vertical direction at all times. Accordingly, the reaction force imparted to the operator when the vertical arm is moved forwardly and backwardly is much smaller than that imparted to him when the horizontal arm is moved up and down or right and left. Another reason is that the provision of the counterbalance mechanism makes the manipulator intricate in construction and increases the weight thereof thereby lowering the operability of the manipulator.
In a conventional counterbalance mechanism, the end of the horizontal arm is lifted through a gimbal mechanism by a balance bar. As the fulcrum of the balance bar is above the center of rotation of the horizontal arm, the balance bar can turn while being rotated in a vertical or horizontal direction with respect to the horizontal arm. In addition, the balance bar is provided with a weight on the opposite side of the suspension point with respect to the fulcrum in order to balance the weight of the manipulator.
FIG. 1 shows an example of a conventional counterbalance mechanism. Such a conventional counterbalance mechanism is described in detail in U.S. Pat. No. 3,913,582 issued to the Laser Industry Co. and Japanese Laid-Open Patent Application Ser. No. 94182/1974 and therefore it will be only described briefly here. A shaft 2 is disposed in a sleeve 1 in such a manner as to be movable vertically. A laser rack 3 is secured to the top of the shaft 2, and a CO.sub.2 laser source 4 is mounted on the laser rack 3. A laser beam from the laser emitting outlet laser source is directed along the axis of a first arm 61 of a manipulator, that is, in the vertical direction.
The manipulator includes seven articulations 51 through 57 each provided with a reflecting mirror, arms 61 through 67 connecting the articulations, and a handpiece 7. Each of the articulations is designed so that it can turn around the axis of the corresponding arm as indicated by arrows. A focusing lens (not shown) is provided in the handpiece 7 to focus the laser beam at a focal point F. The operation of the manipulator thus constructed is as described above.
The prior art counterbalance mechanism will next be described. A support 6 fixedly secured to the top of the first articulator 51 of the manipulator has a pin 8 which is provided on a horizontal axis 10. A balance bar 12 is coupled through the pin 8 to the support 6 in such a manner that it can turn around the horizontal axis 10. A gimbal mechanism 14 for lifting the third arm 63 is provided at a point 13 on one end of the balance bar 12. The coupling position of the gimbal mechanism 14 is before the rotary cylinder 5 of the articulation 53. A weight 15 is secured to the other end of the balance bar 12. The weight 15 is heavy enough to balance the weight of the manipulator so that normally the third arm 63 is maintained substantially horizontal in a neutral position. The axis of the pin 8, namely the horizontal axis 10, intersects at a right angle with the axis of the first arm 61 which is rotatable around its vertical axis. Therefore the third arm 63 can turn freely around the horizontal axis 10 and around the first arm 61 in both vertical and horizontal directions. The reason why the gimbal mechanism 14 is provided is as follows. The arm 63 has a different rotational center and radius of rotation in the vertical and horizontal directions from the balance bar 12 and therefore the arm 63 is different from the balance bar 12 as to the rotational angle as a result of which a twisting moment results at the suspension point 14a. The gimbal mechanism is provided to absorb this twisting moment.
The above-described system is disadvantageous in the following points.
(1) Since the balance fulcrum is above the axis of rotation of the horizontal arm, the total height of the laser knife device is increased a corresponding amount. When the end of the horizontal arm is lowered, the weight is lifted upwardly as a result of which the total height of the laser knife device is further increased. As was described before, it is desirable that the maximum height of the balance mechanism or the laser knife device be sufficiently low that the balance mechanism or the laser knife device cannot be brought into contact with an overhead lamp.
(2) A second disadvantage of the system relates to the position of the horizontal arm suspended by the balance bar and the technique used, for suspending the horizontal arm from the balance bar. According to the most frequently used system, a mirror articulation connected to the end of the horizontal arm is so designed that its junction is rotatable. Therefore, the suspension position of the balance bar is before the rotating part and the horizontal bar is lifted directly by the balance bar. Accordingly, a part of the manipulator which is attached to the suspending part may be bent. Since the horizontal arm turns both vertically and horizontally, it cannot be firmly coupled to the balance bar. That is, the horizontal bar must be suspended by means of a gimbal mechanism as a result of which the structure of the counterbalance mechanism becomes unavoidably intricate. Furthermore, according to this technique, the horizontal arm is lifted upwardly. When the horizontal arm is moved upwardly, it may be brought into contact with the overhead operating lamp.
The disadvantages of the conventional counterbalance can be summarized as follows. (1) As the fulcrum of the counter-balance is high, the total height of the laser knife is unavoidably high. (2) As the suspension technique used is not suitable, the optical axis of the manipulator may be disturbed.
Accordingly, an object of the present invention is to provide a counterbalance mechanism for a laser knife device in which all of the above-described difficulties have been eliminated and in which (1) moment-free operation of the manipulator is provided, (2) a suspension device which prevents bending of the manipulator is provided, (3) the total height of the laser knife device is limited to the extent that it will not strike adjacent structures such as the overhead operating lamp, and (4) the external appearance of the mechanism is simple so that the mechanism does not disturb the operator and is simple in construction and low in manufacturing cost.